Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
  • G06F21/60—Protecting data
  • G06F21/64—Protecting data integrity, e.g. using checksums, certificates or signatures
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
  • H04L9/3236—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials using cryptographic hash functions
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/32—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials
  • H04L9/3247—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols including means for verifying the identity or authority of a user of the system or for message authentication, e.g. authorization, entity authentication, data integrity or data verification, non-repudiation, key authentication or verification of credentials involving digital signatures
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
  • H04L2209/60—Digital content management, e.g. content distribution

Definitions

• Obtaining a person's hand-written signature is a traditional and useful technique to establish identity and will of the person (a signatory) to execute a document (e.g., a record, contract, memorandum, etc.), and a willingness of the person to be bound by content of the document. Even in this digital age, hand- written signatures are a necessary part of legal agreements, bank and credit card transactions, and contracts of all kinds.
• a person hand-signs a document electronically e.g., with a pen attached to a pen pad device such as a graphics pad, a tablet PC, etc.
• a digital image e.g., a JPEG, TIFF, or other image type
• the digital image of the hand-written signature is an electronic signature that is a legally binding equivalent of the individual's handwritten signature.
• image processing software a person's electronic signature can typically be cut/copied from a document and pasted/copied into a different document for unauthorized use.
• unauthorized use includes, for example, forgery, spoofing consent, etc.
• the rapidly rising problem of identity theft illustrates the ease of unauthorized uses of electronic signatures.
• a secure signature is generated.
• the secure signature strongly binds an image of an electronic signature (an "electronic signature") to content in either electronic or printed form.
• an electronic signature an "electronic signature”
• Responsive to receiving a request from a user the systems and methods determine whether an electronic signature associated with a printed page represents a secure signature. If so, the systems and methods determine and notify the user of whether the secure signature was cryptographically bound by a signer of the electronic signature to the content being signed.
• Fig. 1 shows an exemplary system for secure signatures, according to one embodiment.
• Fig. 2 shows an exemplary procedure for secure signatures, according to one embodiment.
• FIG. 3 shows further operations of the exemplary procedure of Fig. 2 for secure signatures, according to one embodiment.
• the systems and methods add security to a digital image of a hand-written signature of a person (i.e., an "electronic signature"), by binding or tying the electronic signature to specific content of the particular digital document being signed. As described below, this also binds a printed version of the electronic signature image (ink/toner at this point) to a printed version of the electronic document.
• the systems and methods generate a first collision resistant hash from a combination of the person's electronic signature and content of the electronically signed document. Using a private key of the person/signer, the systems and methods digitally sign the collision resistant hash using one of multiple possible public-key cryptographic techniques.
• the systems and methods insert/embed the public-key digital signature into the bits associated with the electronic signature to generate a "secure signature".
• the secure signature comprises a digitally signed fingerprint of the electronic signature together with the original document content that can only be decrypted using the person's public key of the private/public key pair. This secure signature binds the person's signature to the content. At this point, the document can be distributed to end-users for viewing and printing.
• a secure signature includes a public-key digital signature of a hash value generated from the person's electronic signature and the content of the document actually signed by the person. (If the document comprising the signature is a paper/printed document, the document is scanned to generate an electronic document representing the printed document). If the systems and methods do not detect such an embedded public-key digital signature in a digital image of the signature (i.e., the signature is not a secure signature), the systems and methods will not verify that the electronic signature authentically binds the signer to content of the document.
• a person's signature could be forged by printing a document comprising a digital image of a secure signature, and tracing over the printed version of the digital image to generate a "clean" signature.
• the "clean" signature will not contain the programmatically detectable and embedded public-key digital signature of the signer that ties the signer's signature to specific content of a document.
• the signature represents a secure signature.
• the extracted public-key digital signature is then decrypted using the public key (of a private/public key pair) of the person/signer.
• the systems and methods compute a second collision resistant hash of the document content (in this example, the document content comprises a digital image of the person's hand-written signature (i.e., an electronic signature) minus the extracted public-key digital signature). If the first and second hashes match, then the systems and methods verify that the person's signature represents intent by the person to execute the document; otherwise such a relationship is not verified.
• Fig. 1 shows an exemplary system 100 for secure signatures, according to one embodiment.
• system 100 includes a computing device 102 such as a general purpose computing device, a server, a laptop, a mobile computing device, a tablet PC, and/or so on.
• a tablet PC typically includes a touch screen or digitizing tablet technology allowing a user to operate the computer with a stylus or digital pen instead of a keyboard or mouse.
• computing device 102 is coupled to an I/O device 104 such as a graphics tablet that allows a user to provide/draw a hand-written signature using a stylus (a pen-like drawing apparatus), similar to the way one draws images with a pencil and paper.
• I/O device 104 such as a graphics tablet that allows a user to provide/draw a hand-written signature using a stylus (a pen-like drawing apparatus), similar to the way one draws images with a pencil and paper.
• Computing device 102 includes one or more processors 106 coupled to a respective tangible computer-readable storage medium such as system memory 108.
• a processor 106 may be a microprocessor, microcomputer, microcontroller, digital signal processor, etc.
• System memory 108 includes, for example, volatile random access memory (e.g., RAM) and non-volatile read-only memory (e.g., ROM, flash memory, etc.) for computer-program instructions executable by a processor 106 and program data generated and/or used by the computer-program instructions.
• Such computer-program instructions are shown as program modules 110 and program data is shown as program data 112.
• program modules 110 include secure hand-written signatures module 114 and other program modules 116 such as an Operating System (OS) to provide a runtime environment, public key cryptographic application ⁇ ), device drivers, etc.
• OS Operating System
• Secure hand-written signatures module 114 (hereinafter often referred to as “secure signatures module 114") generates a secure signature 118 that cryptographically binds a persons's electronic signature to content of a document 120 (e.g., one or more pages of content representing a record, a contract, and memorandum, official stationery, etc.).
• An electronic signature represents a digital image version of a hand- written signature of the person (also referred to as the "signer”).
• Such an electronic signature is shown as a respective portion of "other program data” 124.
• secure signatures module 114 receives an electronic signature from an I/O device such as a card reader, a graphics pad, etc.
• a person generates an electronic signature using a pen/stylus attached to a digital pen pad device (e.g., a graphics pad, a tablet PC, etc.).
• a digital pen pad device e.g., a graphics pad, a tablet PC, etc.
• the electronic signature is attached or otherwise logically associated with document 120.
• the electronic signature represents a willingness of the user to execute content of document 120 (i.e., a willingness of the user to be bound by content of document 120).
• secure signatures module 114 creates a secure signature 118 that cryptographically ties/binds the user's electronic signature to content of document 120 as follows.
• D be a bitmap of an original document 120 that was electronically signed by a user.
• secure signatures module 114 uses one of multiple possible known collision resistant cryptographic hash functions (e.g., SHA 1, etc.) to generate h(D), which is a collision resistant cryptographic hash ("hash 126") of D.
• secure signatures module 114 generates h(D) from the signer's electronic signature and content of the document 120.
• secure signatures module 114 uses a public-key cryptographic application/infrastructure (e.g., RSA 5 DSA, ECDSA, BLS, etc.) and a private key of the user/signer, secure signatures module 114 computes a public-key digital signature 122 (R) from h(D) (note that at this juncture the claimed identity of the signer is verified by the system using the public-key infrastructure). That is, secure signatures module 114 cryptographically signs h(D) to generate R. Secure signatures module 114 then generates secure signature 118 by inserting/embedding or logically associating R (122) into the bits of the electronic signature. In this manner, secure signature 118 cryptographically ties/binds the electronic signature to content of document 120.
• a public-key cryptographic application/infrastructure e.g., RSA 5 DSA, ECDSA, BLS, etc.
• secure signatures module 114 inserts/embeds (or logically associates) R (122) into the image of electronic signature 118 using a Least Significant Bit (LSB) rriap technique to preserve readability and legibility of secure signature 118.
• LSB Least Significant Bit
• such an LSB mapping technique creates a faint grayscale image (hash pattern) that encodes values of R. This two-dimensional pattern would be nearly imperceptible to an untrained eye. This two- dimensional pattern, however, can be programmatically identified and extracted from a screen capture or a printed image in a way that could be reconstructed and verified against document content.
• secure signatures 114 creates secure signature 118 by embedding R (122) into an electronic signature such that R is visually unobtrusive (e.g., hidden, or invisible) to a viewer.
• R is visually unobtrusive
• a user if a user generates a printed document 128 from document 120, the R embedded in the secure signature 118 associated with document 120 is still embedded and represented in the ink/toner version of the secure signature on a page of the printed document 128.
• signature verification module 130 can detect and extract R from a scanned in bitmap (document D') of the printed document 128.
• a user verifies whether a signer's electronic signature (encapsulated by a secure signature 118) authentically binds the signer to content of a document (i.e., the electronic signature has not been forged, cut and paste, etc., into the document) by interfacing with secure signature validation module 130 of system 100.
• the user may be interfacing with computing device 102 or remote computing device 136 coupled across a network 132 to computing device 102.
• Network 132 may include any combination of a local area network (LAN) and a general wide area network (WAN) communication environments, such as those which are commonplace in offices, enterprise- wide computer networks, intranets, and the Internet).
• secure signature validation module 130 communicates a user interface (UI) and/or webpages to the user.
• UI user interface
• Such a UI and webpages allow the user to specify a document D' comprise an electronic signature and a public key of a purported signer of a secure signature 118 comprising the electronic signature.
• the document comprising the signature is a paper/printed document 128, the user scans the printed document 128 to generate an electronic document D').
• a public key and D' are represented or specified via request 140 from remote computing device 136.
• Signature verification 130 locates a bitmap representing the hand-written signature portion of D'.
• a user/operator manually identifies the bits associated with signature (e.g., draws a rectangle with a pointing device to define dimensions of the bitmap, etc.).
• the identified signature bits comprise a secure signature 118 or a plain, conventional digital image of a person's handwritten signature.
• a forger tracing over a printed version of a secure signature 118 can at most generate an electronic signature.
• Such a forged signature will not comprise the programmatically detectable and embedded public-key digital signature of the actual/real signer that is in the printed version of the secure signature 118.
• Secure signature verification 130 attempts to extract a public-key digital signature R (122) from the bits associated with the electronic signature. In one implementation, this is accomplished by reading off the least significant bits of the pixel intensity values associated with the identified portion. If a public-key digital signature R is not present, the electronic signature in the identified portion is not a secure signature HS (i.e., there is no cryptographic tie of the electronic signature to content of D') and module 130 notifies the user that authenticity of the signature with respect to the content of document D' cannot be verified.
• a public-key digital signature R is not present, the electronic signature in the identified portion is not a secure signature HS (i.e., there is no cryptographic tie of the electronic signature to content of D') and module 130 notifies the user that authenticity of the signature with respect to the content of document D' cannot be verified.
• a digital signature R is extracted from the electronic signature in the identified portion, the electronic signature is a secure signature 118.
• the extraction operations clear/zero-out the pixel intensity values in the identified secure signature 118, resulting in a plain electronic signature.
• the signature verification follows the digital signature protocol selected for the scheme.
• signature validation 130 decrypts the extracted digital signature R using the received public-key to identify a first collision resistant cryptographic hash value h(D) 126. In one implementation, in the case of an RSA digital signature R, this would involve exponentiation of R using the public key of the signer and a check/evaluation to see if the result matches the published certificate/key of the signer.
• Signature verification 130 then computes a second collision resistant hash h(D') of D', which comprises the content and the electronic signature. (At the point that h(D 3 ) is calculated, D' still includes the electronic signature 118, but the electronic signature is no longer a secure signature 118 in that it no longer comprises an embedded digital signature R).
• Signature validation logic 130 compares the first and second hash values 126. If the first and second hash values 126 are the same, signature validation 130 notifies the user that the electronic signature encapsulated in the secure signature 118 represents a willingness of the author/signer to be bound to the content of D'. Otherwise, signature validation 130 notifies the user that electronic signature does not represent a willingness of the author/signer to be bound to the content of D'.
• Fig. 2 shows an exemplary procedure 200 for secure signatures, according to one embodiment.
• operations of procedure 200 are described with respect to certain components of Fig. 1.
• the leftmost numeral of a reference number indicates the particular figure where the component was first introduced.
• respective ones of secure signature module 114 and secure verification module 130 implement the operations of procedure 200.
• Operations at block 202 receive an electronic signature from a signatory/signer indicating execution of a document 120.
• Operations of block 204 augment the electronic signature to generate a secure signature 118 that cryptographically ties the electronic signature to content of the document 120. In one implementation, this is accomplished by generating a collision resistant hash from content of document 120 and the electronic signature.
• This collision resistant hash is then cryptographically signed using a public-key cryptographic infrastructure to generate a public-key digital signature 122.
• the operations of block 204 insert the public-key digital signature 122 into the electronic signature 118 to generate the secure signature 118.
• secure signature 118 cryptographically ties/binds a signers' electronic signature to specific content of document 120. For instance, a secure signature 118 cut from an original document and pasted into a different document will not be cryptographically tied to the content of the different document.
• Operations at block 208 receive a request to verify whether an electronic signature of a signer is securely tied/bound to content of a document D'.
• the request includes (or otherwise identifies) the document D' to be verified as well as a public key of a private/public cryptographic key pair of the purported document signer.
• Operations of block 210 attempt to extract a public-key digital signature R (122) from the electronic signature embedded or logically associated with the received document. If such a public-key digital signature R is present in the electronic signature, the electronic signature is a secure signature 118.
• the extraction operations remove/strip-out (e.g., zero-out) any indication R from the electronic signature.
• Operations of block 212 determine if a public-key digital signature R was found in the electronic signature.
• operations of procedure 200 continue at on-page reference "A" of Fig. 3, where the user is notified that electronic signature associated with D' cannot be verified to represent willingness of the signer to execute content of the document D'. Otherwise, operations of block 214 decrypt the extracted public-key digital signature R (122) using the public-key of the signer (the public-key was received in the request associated with operations of block 202). These decryption operations result in a first hash value h(D) 126. Operations of block 216 compute a second hash value 126 (i.e., a collision resistant hash value) from content of the document D' and the electronic signature, which was stripped of the extracted public-key digital signature (please see operations of block 210). At this point, operations of procedure 200 continue at on-page reference "B" of Fig. 3.
• a second hash value 126 i.e., a collision resistant hash value
• FIG. 3 shows further operations of the exemplary procedure 200 of Fig. 2 for secure signatures, according to one embodiment.
• Operations of block 302 compare the first and second hash values 126 (please refer to the previously described operations of block 216 of Fig. 2).
• the first hash value 126 was the result of decrypting the public-key digital signature 122 associated with the secure signature 118 embedded or logically associated with the document D' (120).
• the second hash value 126 was calculated using a collision-resistant hash function from content of document D' and the corresponding electronic signature (the secure signature 118 stripped of the digital signature). If the first hash value 126 is the same as the second hash value 126, operations of block 304 continue at block 306.
• Operations of block 306 notify the user (i.e., the requester of block 202 of Fig. 2) that the electronic signature associated with the document D' represents willingness of the signatory to execute content of the document D'. If the first hash value 126 is not the same as the second hash value 126, operations of block 304 continue at block 308. Operations of block 308 notify the user that the electronic signature associated with the document D' cannot be verified to represent willingness of the signatory to execute (e.g., be bound to) content of the document. At this point, operations of procedure 200 terminate.
• secure signatures has been described in language specific to structural features and/or methodological operations or actions, it is understood that the implementations presented in the appended claims are not necessarily limited to the specific features or actions described above.
• operations associated with secure hand-written signature module 114 (Fig. 1) are shown and described as encapsulating operations for signature verification module/logic 130, operations of these respective program modules can be independent from one another.
• operations of secure hand- written signature module 114 do not encapsulate operations of module 130, but are instead implemented completely independent of such operations.
• operations of module 114 are implemented on a different computing device then operations of module 130. Accordingly, the specific features and operations discussed above are disclosed as exemplary forms of implementing the following claimed subject matter.

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• 2007
  • 2007-04-05 WO PCT/US2007/008678 patent/WO2007127038A2/en active Application Filing
  • 2007-04-05 CA CA002645213A patent/CA2645213A1/en not_active Abandoned
  • 2007-04-05 JP JP2009507701A patent/JP2009535898A/ja active Pending
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